The application of solid-state detectors of high energy resolution to x-ray spectrometry, and the increasing use of compu­ ters in both measurement and data evaluation, are giving a new stimulus to x-ray techniques in analytical chemistry. The Twentieth Annual Denver X-ray Conference reflects this renewed interest in several ways. The invited papers, grouped in Session I, review the charac­ teristics of the detectors used in the measurement of x-rays. One paper is dedicated to the detection of single io.ns. Although such a subject may appear to be marginal to the purposes of the Denver Conference, we must recognize the affinity of techniques applied to similar purposes. Ion probe mass spectrometry is dedicated to tasks similar to those performed by x-ray spectrometry with the electron probe microanalyzer. Scientists and technologists will see these two techniques discussed in the same meetings. The discussion of automation and programming is not limited to the two invited speakers, but extends to papers presented in more than one session. The matter of fluorescence analysis by isotope- and tube-excitation will also be of great interest to those concerned with the practical applications of x-ray techniques. The communications contained in this volume, and the lively discussions which frequently followed the presentation of papers, attest to the vitality of the subjects which are the concern of the Annual Denver X-ray Conference.